Fatty acids containing two or more unsaturated bonds are collectively referred to as polyunsaturated fatty acids (PUFAs) and known to specifically include arachidonic acid (ARA), dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), etc. Some of these polyunsaturated fatty acids cannot be synthesized in the animal body. It is therefore necessary to compensate these polyunsaturated fatty acids as essential amino acids from food.
Polyunsaturated fatty acids are widely distributed; for instance, arachidonic acid can be separated from lipids extracted from the adrenal glands and livers of animals. However, polyunsaturated fatty acids contained in animal organs are only in a small quantity and cannot be obtained sufficiently for large supplies when simply extracted or separated from animal organs. For this reason, microbial techniques have been developed for obtaining polyunsaturated fatty acids by cultivation of various microorganisms. Above all, microorganisms of the genus Mortierella are known to produce lipids containing polyunsaturated fatty acids such as arachidonic acid and the like.
Other attempts have also been made to produce polyunsaturated fatty acids in plants. Polyunsaturated fatty acids constitute storage lipids such as triacylglycerols and are known to be accumulated within microorganism mycelia or plant seeds.
Acyl-CoA synthetase (ACS) is an enzyme catalyzing the thioesterification of fatty acids and coenzyme A (CoA) and catalyzes the following reaction.Fatty acid+CoASH+ATP→Acyl-CoA+AMP+PPi
Acyl-CoA produced by ACS is involved in various life phenomena including the biosynthesis and remodeling of lipids, energy production by β-oxidation, acylation of proteins, expression regulation by fatty acids, etc. Furthermore, ACS is reportedly associated with extracellular uptake of fatty acids, intracellular transport of fatty acids, etc. (Non-Patent Documents 1 and 2). In view of the foregoing, it is considered to control the activity of ACS when polyunsaturated fatty acids or the like are produced by utilizing microorganisms or plants.
In the yeast Saccharomyces cerevisiae used as a model eukaryote, six (6) acyl-CoA synthetase genes (ScFAA1, ScFAA2, ScFAA3, ScFAA4, ScFAT1 and ScFAT2) are known (Non-Patent Document 1). The proteins encoded by these genes are different in substrate specificity, timing of expression, intracellular localization and function.
Patent Document 1 discloses nine (9) genes as the acyl-CoA synthetase gene (ScACS) derived from Schizochytrium sp. Patent Document 1 also discloses an increased production of DPA (n-6) (docosapentanoic acid (n-6)) or DHA when the gene encoding the Schizochytrium sp. PUFA synthase system is co-expressed with ScACS, as compared to the case where the co-expression with ScACS is not involved.
In addition, acyl-CoA synthetase genes derived from animals and plants are also reported (Non-Patent Document 2 and Patent Document 2).    [Patent Document 1] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-529890    [Patent Document 2] PCT International Publication Pamphlet WO 0209295    [Non-Patent Document 1] B. B. A. 1771, 286-298, 2007    [Non-Patent Document 2] Exp. Biol. Med., 233 (5), 507-521, 2008